Ambrx Biopharma has dosed the first subject in its global Phase II clinical trial of an advanced internal candidate, ARX788, in HER2-positive metastatic breast cancer patients.

An anti-HER2 antibody-drug conjugate (ADC), ARX788 is intended to increase the activity of potential anti-tumours by enhancing the payloads and the chemical bonds’ position and number that conjugate the payloads to the antibody.

It comprises two AS269 cytotoxic payloads, which are specifically conjugated to a trastuzumab-based antibody and target the HER2 receptor.

The multicentre ACE-Breast-03 clinical study will assess the safety and efficacy of ARX788 in patients with HER2-positive, metastatic breast cancer.

The disease of these patients is resistant or refractory to T-DM1, and/or T-DXd, and/or – regimens that contain tucatinib.

The objective response rate will be the study’s primary outcome measure.

Ambrx Biopharma president, CEO and Board chairman Feng Tian said: “Dosing the first patient in this Phase 2 study of ARX788 in patients with HER2-positive metastatic breast cancer marks an important milestone for Ambrx.

“We have made excellent progress with our clinical development pipeline over the last few months, highlighted by our positive data of ARX788 for HER2-positive gastric cancer, as well as the dosing of the first patient in a Phase 1 trial of ARX517 for PSMA expressing tumours.

“Our growing clinical programmes, coupled with an influx of capital from our IPO in June 2021, leaves Ambrx well-positioned to potentially attain several near-term clinical and corporate milestones.”

ARX788 is currently being broadly studied for the treatment of gastric/ gastroesophageal junction (GEJ) or breast cancers, as well as other solid tumours.

It received Fast Track Designation for treatment in HER2+ metastatic breast cancer and Orphan Drug Designation in gastric cancer from the US Food and Drug Administration.

Last month, the company announced positive interim data from the Phase I ACE-Gastric-01 clinical trial of ARX788 to treat HER2+ metastatic gastric / GEJ cancer.